Combustion engine pressure control apparatus



Feb. 3, 1953 S. CRUM COMBUSTION ENGINE PRESSURE CONTROL APPARATUS Filed March 29, 1946 2 SHEETS- SHEET l IN VEN TOR. 57E/MFN (WIJ/7 /7 77 Off/Vf Y Feb. 3, 1953 s. CRUM COMBUSTION ENGINE PRESSURE CONTROL APPARATUS Filed Maron 29, i946 2 Sl-iEETS--SHEET 2 /50 A i i l INVENTOR. TEF/E/V CHUM Patenterl Feb. 3, 1953 COllBUSTlr-l ENGNE FRE S SURE GNTROL Al'lARATUS.

Stephen Crum, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company,

minneapolis, Minn., a corporation of Delaware .implicati-on lala-rch 29, 1946, Serial No. 658,360

The present invention is concerned with pressure control apparatus and more particularly apparatus adaptable for use in connection with controlling the pressure ci fluid supplied under pressure to a combustion chamber such as that of an internal combustion engine.

lt is quite common in connection with various types of engines employing combustion chain bers, such as an internal combustion engine, to employ a supercharger for supplying air under pressure to the engine. This is particularly true in connection with aircraft engines which have to operate at relatively high altitudes. A comn mon form of such a supercharger is a turbo supercharger, in which the compressor is driven by a turbine operated by exhaust gases from the coinbustion chamber. In order to control the discharge pressure of the supercharger, it is coini'non to provide apparatus by which the operation of the turbine and hence of the compressor is controlled by a device responsive to the pressure conditions on the discharge side of the supercharger so as to maintain a selected pressure condition at a desired value. A particularly desirable form of such a control is that shown in the patent to Daniel G. Taylor 2,388,359, granted November 6, 1945. In this control, a normally balanced electrical network controls through an electronic amplifier a motor which positions a waste gate of the turbine driving the supercharger. This waste gate, by varying the amount of exhaust gas bypassed around the turbine, varies the speed of the latter and hence of the supercharger. Upon the pressure changing from the selected value, the network is unbalanced in one direction or the other to cause energization of the motor in such a direction as to position the waste gate in a manner to restore the pressure to the desired value. A system such as just described depends for its operation upon the maintenance of electrical power and the proper functioning or" the various electrical de vices. While the possibility of an electrical iailure cr oi the abnormal failure oi the electrical devices is relatively slight, the hazard ci such a failure is sufficiently great that it has been proposed to employ additional means operative inr dependently of the electrical system whenever the pressure on the discharge side of the supercharger exceeds a normal controlling range of values to rcause movement oi the waste gate oi the turbo supercharger towards an open position in which the speed of the turbine and hence of the compressor is reduced. An arrangement of this type is disclosed in the copending application ci Hubert T. Sparrow, Serial No. 536,331, filed May 19, 1944i, now Patent No. 2,433,326, issued December 23, lll-i In this application, an air operated motor is eiiective to adjust the linkage between the waste gate motor and the waste gate to move the waste gate to open position when ever the pressure on the discharge side of the turbo supercharger exceeds a predetermined critical value.

An object of the present invention is to provide an improved apparatus of the type shown in the aiorementioned Sparrow application.

More specifically, an object oi the present invention is to provide apparatus for controlling the pressure oi the air supplied to a combustion chamber by a compressor in which a motor normally positions a speed controller for the co.L presser in accordance with the pressure delivered cy the compressor and in which an auxiliary air operated motor is effective to operate on the shaft of the iirst motor whenever the discharge pressure exceeds a value beyond the normal controlling range.

A further object of the present invention is to provide an arrangement such as set out in the preceding object in which the motor is an electric rnotor and the air motor is an air turbine which is adapted upon the occurrence oi excess pressure conditions to rotate the rotor shaft of the electric motor.

A further object oi the present invention is to provide in connection with such an arrangement, means for preventing too abrupt movement ci the connecting means between the motor and the compressor speed contro er to its end position upon the occurr :ice of excessive pressure ccnditions.

A still further object oi the present invention is to provide means for limiting the pressure differential across the-air motor and hence limiting the power supplied to it.

A further object of the present invention is to provide pressure relief means in connection with the means for supplying air to the air motor for releasing ressurewhenever the differential be- 3 tween the pressure of the air delivered to the air motor and that of the atmosphere exceeds a predetermined value.

A further object of the present invention is to provide a resilient end stop for the electric motor and the air turbine at the low speed end of the range of movement of the motor to prevent an excessive strain being placed on the apparatus due to the rapid operation of the air turbine.

A still further object of the present invention is to provide automatic means for returning the speed controlling means to an intermediate position following its movement to an extreme low speed position as a result of an excessive pressure condition and upon the reduction of said pressure condition to a normal value while said automatically controlled means is still operative.

A further object of the present invention is to provide an improved motor means in which an air operated motor is designed to operate on the same shaft as an electrically operated motor and in which a resilient end stop is provided on the output shaft of the electric motor to absorb the shock resulting from rapid operation of the output shaft to an end position by the air turbine.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims and drawing, of which Figure 1 is a schematic view showing schematically my improved pressure control apparatus associated with an internal combustion engine,

Figure 2 is a vertical sectional View of my iinproved motor unit, and

Figure 3 is an end view of my motor with the end cover removed and with portions broken away.

Referring now more particularly to Figure l, I show therein an engine I6, which may be the engine of an aircraft. Air for supporting combustion in the engine passes from an intake Ii through a compressor l2, a conduit i3, an aftercooler le, a conduit l5, a throttle it, a carburetor Il, a conduit I8, a direct driven compressor Iii, a conduit 2G, and an intake manifold 2l into the engine.

The exhaust gases from the engine issue from an exhaust manifold 22 and are discharged through a duct 23 having a branch 2li leading to a turbine Q5. The turbine is provided with an outlet 26 through which the exhaust gases may escape to atmosphere after passing through the turbine. The conduit 23, commonly termed the exhaust stack, also has an outlet 27 to atmosphere, and controlling the flow of exhaust gases from this outlet is a damper or valve 28 known as the waste gate.

The compressor l2 is driven from the turbine 25 through a shaft 29 and the air compressed in this compressor I 2 passes through the aftercooler I4, wherein the heat of. compression is at least partly removed by passing fresh air from an intake 30 in heat exchanging relation with the compressor discharge air, after which the cooling air is delivered at the outlet 3l.

The throttle It may be adjusted by the hand control 32, and in the carburetor Il fuel from a supply (not here shown) is mixed with the air to form a combustible gas.

The compressor I9 is directly driven from the engine by shaft 33 and is utilized not only as a compressor but also to evenly distribute the mixture of fuel and air to all cylinders of the engine.

The waste gate 28 is driven by a motor 3d through a gear train 35. A shaft Stia is connected to the output of the gear train 35 and a crank arm 34h is secured to the shaft Sila. A link 35o extends frorn the crank arm 3de to a crank arm 35d secured to the waste gate 23. The motor 3d is of the split phase type, being provided with a pair of field windings 36 and 3l which are spaced ninety electrical degrees apart, and an armature 3S. The field winding 3l is supplied with electrical energy from a secondary winding 3.9 of a transformer lil having a primary winding i which is connected to a suitable source (not shown) of alternating current. The energizing circuit for the winding 3l may be traced from the right-hand terminal of the transformer winding 3e through a conductor d2, a condenser 3, a conductor 62a, the held winding El, and conductors and il to the left-hand terminal of the secondary winding 39.

The flow of electrical energy to the motor field winding 3&3 is controlled by an electronic amplifier 5 to which the winding is connected by conductors (it, 4Q, and lec. The ampliiier i5 is powered from another secondary winding i3 on the transformer eil, to which the amplifier is connected through conductors i9 and 5e.

The amplifier i5 is provided with a pair of input terminals 5l and 52 and operates to supply the eld winding 36 of the motor with alternating current the phase of which depends upon the phase of an alternating current signal impressed across these input terminals 5i and 52. Any suitable form of amplier may be used, but I prefer to employ one of the type shown in Fig. 1 of the co-pending application of Albert P. Upton, Serial No. 437,561, filed April 3, 1942, now Patent No. 2,423,534, issued July 8, 1947.

It will be evident that if the motor field winding 3e is supplied with alternating current which leads the current in the other eld winding 31 by ninety electrical degrees the motor will rotate in one direction, whereas if the current in winding 3S lags the current in winding 3l by this amount, the motor will rotate in the opposite direction.

The phase of the signal applied to the ampliiler input terminals 5l and 52 is determined by the electrical conditions existing in a compound network which consists of three separate networks connected in series. The vcircuit between the amplifier input terminals may be traced from terminal 5I through a conductor 53, a first electrical network Ell, a conductor 55, a second electrical network 56, a conductor El, a third electrical network 53, and a conductor 53, back to the input terminal 52.

The network E8 includes a transformer 6E? having a primary winding fica and a secondary winding Gilb across the terminals of which is connected a slidewire resistance 6 i by means of conductors 62 and 63. The conductor 59 is connected to a slider Eil which cooperates with the resistance Si and which is adjustable thereacross by means of a control knob 35. The resistance 6l and slider tl together form a control point adjuster 56 or manual selector for the intake manifold pressure control system.

Another slidewire resistance 57 is connected across one-half of the transformer secondary winding Elib by a conductor E38 connected to a lower terminal thereof and a conductor 59 connected to a center tap on the winding. A slider lil cooperates with the resistance 6l to form a Calibrating potentiometer designated generally at ll. The center tap of the winding Elib is connected by a conductor l2 to the center of the resistance 9| to decrease the impedance between the sliders 84 and 19.

The network 56 comprises a transformer 13 having a primary winding 13a and a secondary winding 13b across the terminals of which is connected a slidewire resistance 14 by means of conductors 15 and 16. Cooperating with this resistance 14 is a slider 11 which is connected to slider 19 by a conductor 51. The slider 11 and the resistance 14 together form a main pressure controller represented generally at 18, and this controller is adjusted in accordance with the pressure in the induction system of the engine. For this purpose a pressure take-off duct 19 is connected to any suitable point between the supercharging compressor l2 and the engine, and is here shown as connected to the duct |5 leading to the throttle l5. The duct 19 conveys the air pressure to the interior of a bellows 89. A second bellows 8| is evacuated and the two bellows 80 and 8| are supported with their free ends extending toward each other at opposite sides of the slider 11. These free ends are connected by link 82' to each other and to the slider 11 so that expansion and contraction of the bellows 88 in response to fluctuations in air pressure therein will shift the slider along the resistance 14. The evacuated bellows 9| compensates this controller for variations in atmospheric pressure in a well known manner.

The network 54 includes a transformer 99 having a primary winding 99a and a secondary winding 95h. A slidewire resistance 9| is connected by conductor 92 to one terminal of secondary winding 99h and by a conductor 93 to an interi;

mediate point or tap 99 on the winding. A slider .94 cooperates with the resistance 9| and is connested to the slider 11 by the aforesaid conductor 55. The slider 94 and resistance 9| cooperate to form a velocity responsive compensating controller 95, and the slider 94 is positioned by a velocity responsive control device 96 connected to and operated by the turbine 25. The slider 94 is moved over the resistance 9| by the control device 98 in accordance with theV velocity of the turbine. lt may be noted that thevslider 94 will normally remain in the position shown upon a conductive` bar 89 at the right-hand end of resistance 9|, but will swing to the left upon the velocity of the turbine exceeding a predetermined y value. The bar 89is provided so that minor accelerations of the turbine will have no effect upon the system.

The network 54| also includes a slidewire resistance 91, the left-hand terminal of which is connected by a conductor 98 to the conductor 93 leading to the intermediate tap 99 on winding 99h and the right-hand terminal of which is connectedby a conductor |89 to the right-hand terminal of winding 98h. A slider IUI to which the aforesaid conductor 53 is connected cooperates with the resistance 91 to form a follow-up potentiometer |92. The slider |01 is moved` along the resistance A91 by a connection to` the shaft 34a, the slider movement being thus concurrent with that of the waste gate 28.

Since the operation of the electrical control system is set out in detail in the aforementioned Taylor patent, it will be only sufficiently described herein to make clear theneedand reason for my present improvements.

The primary windings of all of thetransforn ers 99, 13, and 99 are connectedto the same alterhating-current source as the primary 4| of transformer 99. To simplify the drawing, these connections have been omitted. In actual practice, only one transformer needs to beV employed, secondary windings 60h, 13b, and 99h being formed as additional windings ofy transformer 49. In either case, the alternating potentials at the respective terminals of these transformer windings are at all times in phase with each other. The signal potential impressed across the amplifier input terminals 5| and 52 will thus be the algebraic sum of a number of potentials developed in the three networks 54, 56, and 58.

For convenience in description, the potential conditions existing during a half cycle at which the transformerwindings have the polarities indicated by the legendsV of plus and minus signs will be considered. For a reference potential the conductor 59 is indicated asgrounded, or of zero potential to ground, as shown at |93.,

In the network 58, then, the slider 64 in the position shown is positive with respect to the center tap of the transformer while the slider 10, being at a mid-point along the resistance E1, isat a, negative potential with respect to the center tap. This network is thus seen to introduce a potential into` the series circuit connecting the amplifier input terminals of such polarity that the slider 19 and conductor 51 are negative with respect to grounded conductor 59.

Turning now to the network 5E it will be seen that with the slider 11 in the position shown, this network introducesl into the series circuit a potential equal to the potential of slider 11 with respect to the left terminal of transformer winding 13b. This potential is then such that conductor 55 is positive with respect to slider 11. The potential of conductor 55 with respect to ground depends upon the relative magnitudes of the respectively negative and positive potentials produced by the networks 58 and 58. For convenience this potential may be considered to be such that conductor 55 is positive with respect to grounded conductor 59.

Considering finally the network 54, it will be evident that since slider 941s at the right-hand extremity of the resistance 9|, the conductor 93 leading to the tap in the transformer winding 9U is at the same (positive) potential with respect to ground as is the conductor 55, leading to this network. The resistance 91 being connected between this point, or conductor 93, andthe now negative terminal of the winding b, the conductor 53 thusis negative with respect` to conductor 93 by an amount dependent upon the value of the resistance between slider IUI and conductor 98. Thus network 54 introduces a negative potential into the series circuit and under a condition of balance the magnitude of this negative potential is equal to and opposes the positive potential produced by the algebraic sum of the effects of networks 56 and 58.

Under such conditions the amplifier input terminal 5| is at the same ground potential as is terminal 52, no signal is then impressed in the amplier and the amplifier supplies no current to the motor field winding 36. The waste gate 28. then remains stationary. However, should any of the sliders beshifted from their positions at which the compound network is balanced a signal potential will develop across the amplifier input terminals resulting in the supply of an operating current to the motor eld winding 35 such as to cause the motor 34 to rotate and change the position of the waste gate.

For example, consider the result of a rise in pressure in the engine induction system. The

bellows 8|! is then expanded and the slider 'l1 is moved to the left along the resistance 14, reducing the magnitude of the positive potential introduced by the network t into the series circuit. This positive potential is thus made insuiiicient to completely cancel or oppose the sum of the .negative potentials introduced by the networks 58 and Sli and a signal potential appears at the amplifier input terminal 5| such that this terminal is negative with respect to terminal 52. It is assumed that the amplier and motor are properly connected to respond to a signal of this polarity or phase so that the amplifier supplies motor eld winding 36 with analternating current potential of the proper phase relation to cause the motor to rotate in proper direction to move the waste gate 28 toward open position. At the same time the slider 0| is moved toward the left along the resistance Si.

The opening movement oi the waste gate 2t reduces the pressure of the exhaust gases exerted on the turbine 25, causes the speed thereof to decrease and reduces the compressing eiect of the compressor I2. rihe pressure of the air supplied to the engine iii and to bellows Si?, is now reduced and the slider Tl begins to Work back to the right along resistance Hl. rThe movement of the slider itl to the left` along resistance el, coincident with the opening movement of the waste gate 28, introduces a balancing positive potential into the series network and this movement will continue until this balancing potential is exactly equalled by the potential introduced by operation of the controller 'I8 and the series network is again balanced. The motor 3d then stops, leaving the waste gate in the newly selected position.

In similar manner, a decrease in discharge pressure of the supercharger i2 will introduce an opposite potential by action of the controller i3, causing a signal of opposite phase to be applied to the amplier which then runs the motor in the opposite direction to close'the waste gate and boost the pressure. Such operation is accompanied by a rebalancing movement of the slider il?! Yto bring the network to balance again.

The same actions occur upon the movement of either cf the manually adjusted sliders 6:3 and 78, and it will be evident without further description herein that, when properly functioning and energized, the system will permit the selection of any desired discharge pressure for the supercharger under control of control point adjuster et and will maintain such pressure by means of controller 78.

The function of the controller Vse will likewise be apparent, it serving to introduce a potential into the network such as to open the waste gate 23 when the velocity of the turbine exceeds a maximum safe value. Such limiting control 0n the speed of the turbo supercharger unit is eifective so long as the electrical circuit is intact and properly energized, and while conditions throughout are within range 0i control.

if the source of electrical energy fails or if any of the sliders fail to make proper contact with their associated resistors, the waste gate will tend to remain in the position to which it has been moved. Or if the amplifier fails to function properly, the electric motor may drive the waste gate to closed position and maintain it there regardless ofV what value the induction pressure assumes. As a result, the pressure on the discharge side of the supercharger may assume an unsafe value. l Severe damage may result to the i above, I provide a turbine in connection with motor 3d which is effective to rotate the rotor shaft and the gear train to drive the waste gate towards open position upon air being supplied to the turbine supercharger. The details of the motor and the various features of my invention associated with it are shown in Figures 2 and 3. These saine features are shown schematically in Figure l along with the means for supplying air at a controlled pressure to the air turbine. Referring rst to Figure 2, the numeral l0 is employed to designate an air turbine wheel. This air turbine wheel has a body portion having struck out tongues forming turbine blades. The turbine Wheel IIB is secured to a hub member H2. The hub member is in turn secured to a shaft I hl.

Rigidly secured to the shaft Het is a conical oil seal member ||5 which is provided on its right hand conical face with a packing ring HS. The oil seal member I le is adapted to seat on a sleeve Hi secured within the end of a sleeve H8. The inner end of the latter sleeve seats against a shoulder of the motor housing casting H9. A nozzle block l2@ surrounds the sleeve H8 and is held in place by screws |2| which extend through the nozzle block into the housing casting I9. Also held in place by screws |2| is a nozzle plate |22 which has struck out tongues |23 providing means for admitting air through the plate |22 and directing it against the blades Iii of the 'turbine wheel. The nozzle casting |20 is provided with an annular nozzle chamber |265. The nozzle block |253 is also provided with a throat |21 which is aligned with an aperture H28 extending through an enlarged portion |3| of the wall of housing H9. A coupling member lil is secured to the housing i 9 by any suitable fastening means (not shown) and serves as a means for introducing air into the aperture 23 and hence into the nozzle chamber |2l.

The sleeve li' is held in position by screws |32 which extend through a downwardly Vextending lange of the nozzle block |2il and into the sleeve l 7.

The shaft l it for the turbine wheel i is supported on the left hand side of the turbine Wheel by a bearing 22@ mounted within the sleeve On its right hand side, it is supported in a bearing 22| secured within a central aperture of a plate ISLE. The plate |3l-i is mounted against a shoulder portion |35 of the housing casting H9, being held in place by a sleeve |36 which abuts against plate i3d. Abutting against the right hand end of body portion ||9 of the sleeve |35 is a diaphragm I3?. A stud member |38 extends through the plurality of backing plates secured on opposite sides of the diaphragm and is adapted to engage the right hand end of shaft it. A clip member |39 secured to stud member |33 extends into a slot adjacent the end of shaft H4 and retains the latter in engagement with stud |38. Enclosing the diaphragm and forming an air chamber therewith is a cap member Idil which has a throat portion |ll| communicating with a passage |42 through the enlarged portion |3| of the body housing. A spring |45 biases the diaphragm and shaft IM to the right. It will be obvious that air pressure admitted on the right acer/,evo

hand side of the diaphragm is eiective to exer a pressure overcoming the biasing action of spring |65. As will be explained later, upon the admission oi air to the on the right hand of the diaphragm, the diaphragm is eiiective to force shaft i4 to the left. This movement of diaphragm |31 to the lei t is limited by a plurality of circumierentially disposed stop pins ifll secured to the plate it, only one of which appears in the drawing. Slidably secured on the air turbine shaft is a clutch member ill-8 which is adapted to engage with a clutch member lait carried by a hollow rotor shaft |5|. The oil seal member l |5 and the clutch member Hi8 are spring pressed apart by a spring |55 and are limited in their relative movement by screws |555 wl ch er1 tend slidably through the clutch member are screw threadedly secured to the oil seal mes. ber lib. Upon inward movement ci the dia phragm |l due to entering the chamber on the right hand side thereof, the air turbine shaft le is moved to the left sufficiently to bring clutch members le@ and les into engagement. This engagement of these clutch members taires place before diaphragm i3? has engaged the stops ifi?. The continued movement of the diaphragm after such engagement taires place causes the air turbine shaft EM to slide with respect to the clutch member |68 against the action of the biasing spring |55 between clutch member and the oil seal member until diaphragm I3? engages the stop pins Uil. rhis causes the biasing spring |55 to exert a force holding the two clutching members Hi8 and ital@ in clutching engagement with each other. By providing the stop pins [e1 to limit the movement of the diaphragm, a uniform pressure is exerted upon the clutch members at all diierential air pressures above the minimum at which the diaphragm is operated.

Slotted apertures |51 are provided at circumferentially spaced points in the motor housing adjacent the air turbine lo to permit the escape of air from the housing as the air leaves the turbine blades. Similar apertures |58 are provided through the motor housing on the left hand side of the diaphragm |31 to permit free movement of the diaphragm |31.

The details oi the electric motor 35| form no part of the present invention. The rotor 3B, as previously indicated, is secured to a hollow shaft |5|. Surrounding the rotor 38 is a stator 3@ of conventional construction on which the eld coils 35 and 31 are secured. A partition wall |68 formed integrally with the motor housing ili separates the portion of the housing containing the rotor and stator from the portion of the motor just described. A bearing member iti is secured within a central aperture in this partition wall and serves to support the rotor shaft Also secured within the partition wall Hill is an oil retainer N32 of conventional construction. Extending through the hollow rotor shaft |5| is a solid shaft |63. The hollow shaft and solid shaft are secured in driving relation with each other by a slip clutch Hifi which consists of a member |55 rigidly secured to shaft H53 and a member Eea adapted to be pressed into engagement therewith by a spring |51. The member |56 is non-rotatably secured te a shoulder at the left hand end of the hollow shaft |55! in such a manner as to be slidable longitudinally but nonrotatable with respect thereto. The function of the slip clutch it is to permit relative slippage or the rotor shaft |I5| and the shaft |63 when the movement of the shaft |63 is stopped. The shaft |63 is operatively connected to the gear train 35. The details of this gear train form no part of my invention. The gear train is partially supported by and separated from the rotor 'and stator by a partition plate |1| which also serves to support a bearing |10 for the shaft |63. The gear train is located within a separate section |12 of the motor housing and the partition plate |1l is clamped between the housing member l i9 and -housing member |12. The housing containing gear train 35 and the chamber enclosing the motor and stator preferably contain oil t0 an approximate depth indicated by the line |13. This oil is fed to the various elements of the gear train and to the rotor shaft. it is prevented to a large extent from passing out into the compartment housing the clutch members m3 and |49 by the oil retainer |52. A certain amount of oil will tend to pass through this oil retainer as the latter is subject to wear, however. The stationary oil seal provided by the engagement of oil seal member H5 with the conical surface of flange ||1 prevents any such oil that might pass through oil retainer |52 from passing out into the compartment housing the air turbine wheel I0.

Electrical power is supplied to the field windings 35 and 31 through an oil tight terminal bloclc |13. Conductors are led to this block through a grommet |19.

The housing |12 is provided with an end wall |323 which serves to help support the gear train to support the output shaft 34a, to which is secured the crank arm 34h previously mentioned.

As best indicated in Figure 3, a laminated stop plate |82 is secured to the shaft 34a. Secured to the stop plate is a laminated V-shaped contact arm assembly Il which slidably engages the potentiometer winding 91 secured to a plate |86.

The stop plate |82 has a relatively wide centrai portion secured to the shaft 34a and a pair of oppositely extending integral wing portions |81 and les. These wing portions extend from a point on the stop plate |82 which is circumferentially spaced from its central portion. The wing portions are considerably elongated, and conform generally to the central portion of the stop plate |82 but are spaced therefrom. The eX- tremities of the wing portion `are spaced laterally from the sides of the central portion of plate |82 by relatively small gaps as shown in the drawing. A stop member |89 is rigidly secured to the housing |12 and is so positioned as to be engaged by the outer extremity of the wing portion |88 upon continued clockwise rotation of shaft 35a, as viewed in Figures 1 and 3. The corresponding outer extremity of wing portion |81 is adapted to engage a pivote/j stop arm |90 which is pivctally secured to the housing |12 by a screw |S|. The stop member |9| is biased in a clockwise direction by a spring |92 which is secured to the housing by a screw fastened spring retainer H33. The left hand end of the spring |92 is secured to the stop member i. Stop member |90 is provided with a slot |952 through which extends a stud screw |95. llhe stud screw |95 serves to limit the outward travel of stop arm |90 and also serves to limit its inward movement by spring m2. A roller |98 is carried by the stop arm |92 and engages the outer end of wing portion |81. The elements are shown in Figure 3 in the position which they occupy when the shaft 34a has rotated in a counter-clockwise direction as far ll as is permitted by the stop member |90. It will be noted that the wing |81 has engaged the roller |98 of stop member |90 and has moved the latter in a counter-clockwise direction against the action of spring |92 as far as is permitted by stud 95.

The wing portions |37 and |38 are slightly resilient and provide, in themselves, a cushioning action when the shaft 34a is rotated to either extreme position. In the case of stop |39, this is all ofthe cushioning action that is provided. In the case of stop plate 9i), the spring 92 provides an additional cushioning action, as will be explained later. Upon the motor reaching either end position, the friction clutch |54 permits continued rotation of rotor 38 and hence avoids any strain on the electric motor or on the air turbine.

Referring back to Figure l, the means for supplying air to the air turbine and the diaphragm |37 will now be described. Connected to the conduit It extending between the supercharger and the after cooler is an air tight housing 29d of a pressure relief valve |99. The connection between conduit i3 and housing Zell is made by a conduit 2M. VLocated within housing 2G53 is a bellows member 2&2 which positions a valve seating on a valve seat communicating with an aperture extending out of the bottom wall of housing Eet. The bellows 22 is biased by an internal spring (not shown) to a position in which the valve 253 is in engagement with its seat. An adjusting screw Z extends through the upper wall of the housing E and serves to variably compress the internal spring to adjust the setting of the bellows 2il2. By reason of the connection of housing Z with conduit i3 through pipe 2M, the exterior of bellows 2Eif'iV is always exposed to the absolute pressure of the air on the discharge side of the supercharger. Whenever this pressure exceeds a predetermined value determined by the setting of screw 265, the bellows 202 is compressed to cause opening of valve 293.

The outlet side of housing 2tlg is connected through a pipe 2e@ with a differential pressure `responsive relief valve 297. This relief valve consists of a housing 298 having an open end 239. Sealing this open end is a ilap valve 2 i il which is pivotally secured to a bracket 2| i extending from the housing 2538. The flap valve is biased to closed position by a spring 2|2, the tension of which is adjusted by a screw 2|3. Whenever the differential between the pressure of the air in the housing 298 and that of the atmosphere exceeds a predetermined value, the flap valve 2m is opened to permit escape of air until the differential returns to the value for which the relief valve is set. Communicating with the relief valve 293 is a conduit 2|5 which is connected tothe nozzle block |26 and the chamber on the right hand side of diaphragm |37. In Figure l, the connections between conduit Ei and the nozzle box and diaphragm chamber are shown schematically.

Operation The normal operation of this system has been described in the previous paragraphs. It will be apparent that normally the waste gate motor 3d is positioned in accordance with the pressure ci the air on the intake side of the carburetor so as to maintain this pressure at a value selected by the pressure selector 5S. In the event of excessive speeds, the pressure is adjusted by the overspeed responsive potentiometer 95. If at any time the waste gate is moved to either extreme position,

l2 the wing portion lil or |87 as the case may be engages its associated stop member, and the motor will continue to revolve by reason of the slippage of clutch |65.

Let it be assumed now that by reason of the` failure of some of the electrical apparatus or more likely by reason of the temporary failure of the power source, the electrical control system for' motor 32 loses control of it or improperly controls it so that the motor 3d remains in the position to which it has been moved. Further, let it be assumed that this position is one in which the waste gate is closed to an extent such that excessively high supercharger discharge pressures will 'be developed at lower altitudes. As the aircraft enters these lower altitudes, the pressure on the discharge side of the supercharger i2 will rise above the setting of the pressure relief valve |9 so as to cause the valve 2GB of the relief valve to be opened. Air Will thereupon be admitted to both the nozzle block E and the chamber on the right hand side of diaphragm i3?. The eifect of the air entering the nozzle block |26 will be to cause the air turbine l i il to be operated at a relatively high speed. The effect of the air entering the chamber on the right hand side of diaphragn |37 will be to cause the diaphragm to move clutch member U53 to the left into engagement with clutch member |49. rIhis engagement of clutch members M6 and |69 causes the turbine |||J to be operatively connected to rotor 38. As previously explained, the blades of the turbine are so designed that the turbine rotates in a direction to move the waste gate 2S towards open position. In other words, the crank Stb will be rotated in a counterclockwise direction as viewed in Figure l. The turbine is capable of overpowering the rotor if it is tending to drive in waste gate closed direction. This will cause movement of the sliderV mi with respect to the resistor Q'i and will also cause movement or" stop plate |32 in a counterclockwise direction so that the Wing portion i8? engages the stop arm |98. If by any chance, the fault of the system lies solely in the contact arm lili resting upon a dead or dirty spot of resistor 9i, the movement on contact arm lei may result in its moving to a position at which the circuit between contact arm itl and resistor Q? is reestablished, thus reestablishing the control of the electrical system over the motor 35i. Since, under these circumstances, the effect of the electrical system would be to drive the motor at to waste gate open position, the motor Se will assist the air turbine and a rapid movement of the waste gate towards open position will result.

Regardless of whether the fault lies in a faulty contact between slider it! and resistor the air turbine will be eifective to cause continued rotation of the shaft 36d and stop plate l? in a counter-clockwise direction. The wing portion E81 will engage the stop arm gil and will move this stop arm in a counterclockwise direction against the action of spring |2. Normally, this movement will occur until the arm l has moved to its extreme left hand position in which the stud'lii is in .engagement with the right of slot itil. Y

The movement of the shaft Sta by the turbine i can occur at a relatively rapid rate. By maintaining the air turbine on 'the same shaft as the rotor, I have provided an arrangement in which the entire motor assembly is relatively compact. Furthermore, the slip clutch between the rotor and the gear train is effective to permit slippage between the air turbine and the ouput shaft as well as between the electric rotor and the output shaft. Tiis arrangement has the disadvantage, however, due to the variation in pressure differential across the turbine with variation in altitude, that the air turbine may be revolved with such force as to cause injury to the apparatus associated with the electric motor. This is prevented in my arrangement by the pressure differential relief valve itil and by the yieldable stop lii. Referring to the pressure relief valve 2d?, the valve serves to l t the pre sure which is applied to the air turbine and hence to limit the maximum speed thereof. This has the advantage not only of protecting the various elements of the motor driven by the turbine but also in preventing damage to the turbine itself from an excessive pressure differential being applied thereto.

Th yieldable stop i serves to absorb the shock resulting from the operation of the output shaft 34a by the air turbine at the relatively high speed at which the air turbine is effective. By reason of this spring d, the shock of the opening movement of shaft Sila is absorbed both by the resiliency oi wing portion Sii? of stop plate id? but also by spring EQ2.

rThe yieldable stop lii has a further very irnportant function. As soon as the pressure withe in conduit i3 has dropped below the value at which the relief valve les is set to operate, air is no longer supplied to the turbine and to the diaphragin li'l. The air turbine is thus declutched from the electric motor and hence from the output shaft lied. The spring i92 is designed so as to have sufficient resiliency to rotate the output shaft Bda backwards against the retarding eiiect of the gear train and the inertia of rotor Sii when no torque is being exerted by either the air turbine or by the rotor 3s. Thus, as soon as the pressure within conduit i3 drops below the c itical value, the spring ist? is effective to move the shaft 32a in a clockwise direction (as viewed in Figures l and 3) to cause the waste gate 253 to move partially towards closed position. The slot ist is of such length and the stud l'l is so located that when the stop arm iii-S has moved to if extreme right .Lub hand position, the waste gate will be in a position at which the exhaust gas tends to close the waste gate. As long as the waste gate is in its wide open position, the exhaust gas has no effect upon the position of the waste gate. .fis soon, however, as it is turned away from this open position, the exhaust gas has a tendency to close the waste gate. This effect is aided by the vibration of the engine. Thus, following a rise in pressure to an unduly high value so that the air turbine drives the waste gate to open position, the waste gate is moved back towards closed position first by the spring isi! and then by the effect of the exhaust gases on the waste gate. A power failure, such as leads to the operation of the air turbine, may well occur under conditions in which it is undesirable for the pilot to be deprived of all supercharging effect. By providing the pring it the waste gate is automatically returned gradually to a closed position so as to proviea supercharging effect. Whenever the gate moves too far to closed position, the air turbine will again be brought into operation to cause the waste gate to again be driven towards open position. Thus, despite fact that the electrical system is rendered completely inoperative, the pressure is maintained at a value which will permit operation of the airplane at a pressure which will result in sufficient power being supplied to the airplane for operation under normal conditions. Moreover, provision is made for quickly opening the waste gate completely to reduce the pressure as rapidly as pcssiie when a critical pressure condition exists.

The features of the clutch between the turbine and the electric motor 35i and the oil seal provided by member l l5 and flange l l'l', together with the diaphragm means for operating the same, do not constitute part of my invention but are claimed in a copending application of Willis H. Gille for Motorf filed concurrently herewith Serial No. 658,021, now Patent 2,487,649. For the purposes of the present invention, it is to be noted that the clutch prevents the electric motor from being subjected to the continual load that would be present if the air turbine were permanently connected to the same. At the same time, it makes possible the stationary oil seal between the motor housing and the air turbine housing s0 as to guard against the escape of oil.

It will be seen that I have provided an iinproved arrangement in connection with an automatic control for a compressor whereby in the event of the control system failing to provide against excessive pressure, the pressure is reduced independently of the control system and is maintained at an intermediate value sufficient for normal operation.

While I have shown a specific forni of invention for purposes of illustration, it is to be understood that the invention is to be limited only by the scope of the appended claims.

l claim as my invention:

l. Apparatus for use with an engine having a combustion chamber and a compressor for supplying fair under compression thereto, comprising, in combination, a movable device for controlling the compressing effect of the compressor, a rst motor having a housing and including a drive means operatively connected to said device for positioning said device, means responsive to a pressure condition of the air supplied connected in controlling relation to said first motor to maintain said pressure condition at a predetermined value, an air motor operatively related to said drive means for positioning said device in a direction to decrease the compressing eifect of the compressor in the event the first motor becomes inoperative, means including a valve for admitting air from the compressor to said air motor to cause operation of the same to thereby decrease the compressing effect of said compressor, and resilient stop means including a portion connected to said drive means and a second portion attached to said housing, said stop means portions being engageable with each other when said device is moved to a first predetermined pressure controlling position, one of said portions comprising spring bias means defiectable by the driving force of the air motor to such a point as to permit positioning said `device by said air motor to a predetermined `lower pressure controlling position, said defiectable portion having sufficient power to reposition said device to said rst predetermined pressure controlling lposition when said air motor is inoperative.

2. The apparatus of claim i wherein the air motor is arranged coaxial with said first motor.

3. The apparatus of claim l wherein a pressure relief valve is provided in said means for admitting air to said air motor to thereby pre- 15 vent overspeeding of said air motor due to excess pressure.

4. The apparatus of claim 1 wherein `said spring bias means comprises a movable spring biased lever means and rigid stop means for limiting the movement of said lever means to two xe'd positions.

STEPHEN CRUM.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Name Date MacDonald et a1. Feb. 3, 1914 Number Number Number 

